Incest refers to sex between people who are closely related. DNA testing can help in cases of suspected incest. In most jurisdictions, sex between close relatives is illegal. Depending on the age of the people involved, incest can be also considered child abuse.

Incestuous scenarios- can DNA testing solve them?

The most commonly reported form for of incest is between father and daughter; however, incest between siblings is also argued to be the more common form, in fact, some studies showing this as being the most prevalent. When a woman falls pregnant from an incestuous relation with a father or brother, proving paternity becomes complicated. DNA testing can usually be used to confirm paternity although this is not always straightforward.

If for example, sisters and brother have had sex and the sister falls pregnant, there are only two options:

Either a paternity DNA test between the child born from the incestuous affair and the brother- this is of course, if the alleged father is available for the test. The next option, if the father is not available for the test and if the child born is male, is a Y chromosome test with a male blood relative of the father- ideally a brother. If the child’s Y chromosome matches that of the male blood relative, it would confirm incest. Y chromosome testing is very reliable in that the result is very much a yes or no answer.

Sibling DNA testing can also be an option. If I suspect my mother and her brother (my uncle) had sex, I can consider doing a DNA test with my uncle’s children. My uncle’s (my uncle could also be the alleged father) children are my first cousins; but, if my uncle is actually my father, then that makes my cousins my half siblings. A DNA test will confirm whether we are actually siblings. Extended testing is always recommended in such cases as whichever the case, cousins or siblings, there will be shared DNA. In cases of extended testing, laboratories will test more genetic markers, normally 20 markers instead of 16, to ensure the results are as accurate as possible. Nevertheless, there is no guarantee that this will be conclusive.

DNA testing for suspect cases of incest is rather complex and a very delicate issue. Always discuss your case fully with the DNA testing company.